Shigemoto Group

Molecular Neuroscience

The transmission of information in the brain is controlled and regulated by various functional molecules, including receptors, channels and transporters located on the plasma membrane of neuronal and glial cells. We investigate the functional roles of these molecules in the synaptic transmission, neuronal circuits, systematic organization of the brain and animal behaviors, by analyzing their localization, movements, and functions using morphological, electrophysiological, and molecular biological techniques. Special attentions are being made to combine these different techniques efficiently and elucidate the integrated brain functions.

- Ultrastructural localization and function of glutamate receptors, Ca channels, etc.Ultrastructural analysis of the localization of glutamate and GABA receptors, especially in spatial relation to the synapses, and colocalization of these receptors with various channel molecules regulated by receptor activation. Visualization of these functional molecules in the plastic changes, or pathological conditions, using in vitro model systems as well as in vivo. For example, we have recently found colocalization of various subunits of glutamate and GABA receptors using a newly developed SDS-digested freeze-fracture replica labeling method. This method is highly sensitive and useful for quantification of number and density of receptor and channel molecules.

Glutamate is the major excitatory neurotransmitter in the brain. The ionotropic NMDA and AMPA receptors and the metabotropic kainate receptors are the major receptors activated by Glutamate. We are using freeze fracture replica labeling method in combination with conventional immunoelectron microscopy to understand the precise localization of these molecules. Recently by using replica labeling we estimated the AMPA receptor density to be roughly 1000 receptors/ ?m2 at the climbing fiber purkinje cell synapse. Furthermore by using non stationary fluctuation analysis of the electrophysiological measurements the AMPA receptor density was found to be essentially the same as the one obtained by our replica labeling.

- Mechanisms of long-term memory formation in the cerebellum, amygdala, etc.Using quantitative analyses of receptor/channel localization and synapse ultrastructure combined with different behavioral paradimes, we investigate in vivo molecular mechanisms for long-term memory formation. We are now focusing on motor learning, spatial learning, and emotional memory formation mediated by structural changes in the cerebellum, hippocampus, and amygdala, respectively.

- Left-right asymmetry of hippocampal synapses and spatial learning We are also working on the left-right asymmetry of NMDA receptors and to clarify its physiological significance and mechanism of its formation. The laterality of the brain function is well known in humans but the molecular determinants of this laterality are still largely elusive.